As the value and use of information continues to increase, individuals and businesses seek additional ways to process and store information. One option available to users is information handling systems. An information handling system generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes thereby allowing users to take advantage of the value of the information. Because technology and information handling needs and requirements vary between different users or applications, information handling systems may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated. The variations in information handling systems allow for information handling systems to be general or configured for a specific user or specific use, such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, information handling systems may include a variety of hardware and software components that may be configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems.
One type of information handling system is a computer system. Examples of the computer system include, but are not limited to, mainframes, workstations, servers, personal computers, notebook computers, laptop computers, and personal digital assistants (PDA). Each computer system may include a processor, memory, and storage media such as a hard drive.
As consumer demand has increased for smaller and more compact computer systems, manufacturers strive to implement new methods to meet these demands. One of these methods includes manufacturing circuit boards with narrow copper traces. Given the smaller and more compact size, the traces are typically routed in close proximity (usually above or below) to a voltage or ground plane.
Voltage planes or ground planes on a circuit board are commonly referred to and serve as “reference planes” for traces routed on either side of them. These reference planes can also function to distribute power by carrying current between power sources, such as voltage regulators, and their associated loads, such as processors and chips. Some reference planes will serve as voltage planes (e.g., a plane with a non-zero voltage) and other planes will serve as ground planes. As such, current loads are drawn from a voltage plane and returned to a ground plane to complete an electrical circuit.
However, any large or fast current carried on a plane can cause “noise” to couple to a trace that is routed near the plane. Generally, the noise is most evident when the trace is routed parallel to the direction of the current change. Manufacturers who have attempted to correct this problem typically have installed filters, such as a capacitor or a low-pass filter made from a capacitor and a resistor, on the trace.
Unfortunately, with some circuit boards, the size of filter needed to remove the noise from the trace also blocks some of or the entire signal on the trace. Moreover, the use of series resistors in low-pass filters can change the voltage drop across a diode. Thus, in some instances, the filter will introduce signal errors into the trace.
Other attempts to correct the noise problem include physical modifications to the circuit board or to the information handling system. Modifications include relocating components such that traces avoid routes over high current densities or routing traces perpendicular to current densities. Given the current mechanical or size constraints of some information handling systems, the relocation of components is simply not an option.
In one particular correction attempt, manufacturers routed sensitive traces near ground planes instead of current planes to reduce the amount of induced noise. Because the amount of induced noise is related to the density of current in the plane, this correction assumes that the ground planes in the circuit board have a lower current density than the voltage planes (e.g., there are more ground planes than current planes).